Week 3 - Structure and function of blood vessels Flashcards
What is the function of blood?
transport, protection and homeostasis
in order to achieve this, blood vessels are required
What are blood vessels?
Closed system of tubes where blood goes away from the heart to the organs and is returned back to the heart.
What is pulmonary circulation?
blood to the lungs
What is systemic circulation?
blood to the rest of the body
What are the different types of blood vessels?
Arteries
Arterioles
Capillaries
Venules
Veins
What are the layers of a blood vessel wall?
→ Tunica intima (interna)
→ Tunica media (middle)
→ Tunica externa (adventitia)
What is the tunica intima?
→Innermost layer called endothelium
which inc. thin flattened cells, a basement membrane and internal elastic lamina
Smooth to reduce friction
Secrete locally acting chemical mediators
Basement mem. and lamina provide support to cells
Why is important that the tunica intima has smooth cells?
If the wall of the blood vessel becomes rough for any reason, platelets could start to adhere to it, causing a clot.
What is the tunica media?
The middle layer of blood vessel wall
→ Made of muscle and the connective tissue elastin - this accounts for the variation of different vessels in terms of levels of elastin and muscle in their walls.
→ Muscle arranged in circular direction to regulate the diameter of the blood vessel - controlled by SNS.
→ External elastic lamina separates outer layer from middle layer and provides support.
What is the tunica externa?
The outermost layer of blood vessel wall
→ Made of elastic and collagen fibres (elastic for stretch and collagen to provide support).
→ Also contains nerves and vasa vasorum (in larger vessels = blood vessels supplying to BV’s themselves)
→ Helps to anchor the vessel to the surrounding tissue
Features, structure and function of arteries?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- carry blood away from heart under high pressure
- 15% blood volume
- elastic arteries → largest arteries i.e. aorta
- muscular arteries → tunica media smooth muscle and elastin
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima
- tunica media
- tunica externa (arranged longtudinally)
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ distribute blood to major organs
→ elastic fibres enable vessels to stretch
→ muscular art. can adjust blood flow
Features, structure and function of arterioles?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- deliver blood to the capillaries
- approx. 400 million
- terminal end of arteriole, distal most muscle cell forms the pre-capillary sphincter
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima
- tunica media
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ regulate blood flow to tissues + affect blood pressure
→ pre-capillary sphincter regulates the resistance to blood flow
Features, structure and function of capillaries?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- microcirculation from capillaries to venules
- 20 billion → large surface area
- 5% blood volume
- found near every cell in body
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima but NO MEDIA OR EXTERNA
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ permit exchange of nutrients and waste between blood and tissues
What are fenestrated capillaries?
Found in kidneys, small intestine, ventricles of the brain
They have small pores to allow larger molecules to pass through
What are sinusoid capillaries?
Found in liver
They have large pores to allow proteins to pass through
Features, structure and function of venules?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- collects blood from capillaries to veins
- thin walls, 10-50um in diameter
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima
- tunica media, little smooth muscle
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ exchange of nutrients and waste
Features, structure and function of veins?
𝑭𝒆𝒂𝒕𝒖𝒓𝒆𝒔:
- returns blood back to heart under low pressure
- thin walls
- 0.5mm for small veins ato 3cm in diameter for larger veins
- can stretch
𝑺𝒕𝒓𝒖𝒄𝒕𝒖𝒓𝒆:
- tunica intima thinner than art.
- tunica media thin
- tunica externa thickest layer (containing collagen + elastic fibres)
- valves - thin fold of tunica intima
𝑭𝒖𝒏𝒄𝒕𝒊𝒐𝒏:
→ blood reservoir
→ valves - prevent backflow
What is anastamosis?
A union of branches of 2 or more arteries - alternative route for blood
Why is there no tunica media or externa in the capillaries?
To allow diffusion to take place
Exchange of nutrients and waste products in the tissues.
Allows oxygen into tissues and for carbon dioxide to be returned to lungs
How does venous return occur?
As the veins are a low pressure system, they need assistance to return the blood back to the heart.
They gain assistance through:
→ Skeletal muscle pump - e.g. walking - Skeletal muscle contraction assists with pumping blood back to the heart - valves prevent backflow
→ Respiratory muscle pump - Alternating compression and decompression of veins:
When breathing the diaphragm moves down, reducing pressure in the thorax which increases pressure in the abdominal cavity, compressing the veins so blood moves towards the heart.
What is homeostasis?
A state of steady internal, physical and chemical conditions maintained by living systems for optimal functioning for the organism.
Pre-set normal limits: body temperature, fluid balance, pH, ions (potassium, sodium and calcium) and blood sugar levels.
What does the regular mechanism involve to achieve homeostasis?
Receptor: picks up that things aren’t at correct values → thermoreceptor, mechanoreceptor
Control centre: information enters control centre→ respiratory centre, reninangiotensin system
Effector: target acted on to return to normal state
What is blood flow?
The volume of blood that flows through any given tissue in a given time (mL/min)
Blood flow to individual tissues is dependent on requirements
Speed of blood flow key points?
Speed (velocity) of blood flow is inversely proportional to the cross sectional area.
→ when there is extensive branching, e.g. in the capillaries, the flow is slower however this allows for nutrients and waste products to be exchanged through diffusion
What is haemodynamics?
factors affecting blood flow
What is the definition and equation for cardiac output?
Total blood flow = Cardiac output - volume of blood that circulates through the systemic (pulmonary) blood vessels per minute.
CO = HR X SV
(around 5-6L/min at rest but can go up to around 35L/min if exercising (elite))
Stroke volume definition?
The volume of blood pumped out of the ventricle with one contraction
What 2 factors is cardiac output distribution dependent on?
→ Pressure difference that drives blood through vessel
→ Resistance to blood flow
What is blood viscosity?
Thickness of the blood
What are the 3 components of vascular resistance?
- Size of the lumen
- Blood viscosity
- Total blood vessel length
How does blood viscosity influence vascular resistance?
Increased viscosity → increased resistance to blood flow → decreased blood flow
Might occur due to dehydration or an increase in red blood cells.
How does the total blood vessel length influence vascular resistance?
Resistance to blood flow is proportional to the length of the vessel
→ the longer the vessel the more resistance
How does the size of the lumen influence vascular resistance?
Small lumen → increased resistance to blood flow → decreased blood flow
What is systemic vascular resistance?
(also known as total peripheral resistance)
It is resistance to blood flow offered by systemic vessels.
𝐒𝐦𝐚𝐥𝐥𝐞𝐫 𝐯𝐞𝐬𝐬𝐞𝐥𝐬 → arterioles, venules + capillaries offer 𝒉𝒊𝒈𝒉 𝒓𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 (arterioles key in controlling systematic vascular resistance).
𝐋𝐚𝐫𝐠𝐞𝐫 𝐯𝐞𝐬𝐬𝐞𝐥𝐬 → e.g. veins - offer 𝒍𝒐𝒘𝒆𝒓 𝒓𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 to blood and act as reservoirs for blood and need assistance to move blood back to heart.
Why are arterioles key in controlling SVR?
They have a large amount of smooth muscle within their wall which allows them to open up or to narrow which impacts blood flow.
What is blood pressure?
The pressure exerted on the blood vessel walls - pumping action of the heart when ventricles contract.
- regulation of blood pressure is vital for life
- constant autonomic (neural) and hormonal control
Where is blood pressure the highest?
In the Aorta as it is just leaving the ventricle
What is a usual blood pressure reading?
120mmHg systolic
80mmHg diastolic
(variations in different individuals)
What is mean arterial pressure?
The average pressure flowing through the arteries.
MAP = CO x systemic vascular resistance
How does autonomic control determine blood pressure?
Short-term control of blood pressure
→Controlled by cardiovascular centre in medulla oblongata.
→This impacts on the sympathetic and parasympathetic nervous system as heart rate can change - sympathetic = stimulatory, parasympathetic = inhibitory.
→ Also controlled by vasomotor centre in the medulla oblongata → impacts constriction/dilation of blood vessels (particularly arterioles) and thus systemic vascular resistance
How does hormonal control determine blood pressure?
Through the renin-angiotensin aldosterone system
Process of autonomic control?
(example of homeostasis)
→Baroreceptors (detect pressure) in the arch of aorta + carotid sinus - pick up the stretch on the blood vessel walls.
if…
- ↓ blood pressure - ↓ stretch on blood vessel walls - ↓ signals (via glossopharyngeal and vagus nerves) to the cardiovascular centre - ↓ inhibitory PNS to SA node - ↑ HR which will ↑ CO and thus blood pressure.
Process of renin-angiotensin aldosterone system?
Long-term control of blood pressure
↳↑ BP - ↓ blood flow to the kidneys - cells in the kidney secrete renin into the blood
↳ Renin splits angiotensin, a large protein, into angiotensin I.
↳ Angiotensin I, which is inactive, is split into pieces by angiotensin-converting enzyme into angiotensin II, a hormone which is active.
↳ Angiotensin II causes the muscular walls of small arteries (arterioles) to constrict, ↑ blood pressure by increasing systemic vascular resistance.
↳ AT II also triggers release of hormone aldosterone from adrenal glands and vasopressin from pituitary gland.
What do aldosterone and vasopressin do?
They are hormones that cause the kidneys to retain sodium.
The increased sodium causes water to be retained, thus increasing blood volume and blood pressure.
What are the 3 functions of blood?
↳Transportation - gases (oxygen and carbon dioxide), nutrients, waster products, hormones.
↳Regulation - homeostasis of body fluids, pH, body temperature, blood osmotic pressure (impacts on water content of cells).
↳ Protection - clotting (reduces blood loss), white blood cells (phagocytosis), proteins (antibodies) protect against disease.
What are formed elements divided into?
Platelets
White blood cells → neutrophils, lymphocytes, monocytes, eosinophils, basophils
Red blood cells
What is plasma divided into?
Proteins 7%→Albumins, globulins, fibrinogen
Water 91.5% → Acts as a solvent
Other solutes 1.5% → Electrolytes, nutrients, waste products, regulatory substances
Key features of blood?
↳ specialised connective tissue
↳ denser than water - sticky
↳ approx. 5 litres circulating at any one time
↳ pH 7.35-7.45
↳ temperature - 38degrees
↳ 2 components: blood plasma (55%) and formed elements (cells - 45%)
What proteins are in plasma?
↳Albumins (most numerous) maintain colloid osmotic pressure
↳Globulins (large) → an example of immunoglobulins (antibodies) which help fight disease
↳Fibrinogen is involved in clotting
What function do the electrolytes and gases have in plasma?
They help with cell function, help enzymes catalyse reactions, hormones and waste products
Key points about red blood cells? (erythrocyte)
↳ 4.8-5.4 million per uL of blood
↳ Biconcave disc with no nucleus - allows flexibility
↳ 7-8 um in diameter
Haemoglobin molecule:
↳ Protein (globin) + 4 polypeptide chains with non protein pigment (heam) attaching to each chain
↳ Centre of each heam is an iron Fe2+ which combines reversibly with oxygen
Key points about white blood cells? (leukocytes)
↳ Larger than RBC and less numerous
↳5000-10,000/uL of blood
↳ Have a nucleus
↳ Agranular (cytes) = lymphocytes (B + T cells and Natural Killer Cells) and monocytes
↳ Granular (phils) = neutrophils, eosinophil and basophils
What are the most and least prevalent white blood cells?
Most - Neutrophils (phagocytosis)
Least - Basophils (release histamine + develop into mast cells when leaving blood)
What is the function of eosinophils?
Respond during allergic reactions - dampen histamine
What is the function of lymphocytes?
To mediate the immune response
What is the function of monocytes?
Phagocytosis
Develop into macrophages when leaving the blood
Key features of platelets?
↳150,000 - 400,000/um of blood
↳Cell fragments
↳2-4um in diameter
↳No nucleus
↳Disc shaped
FUNCTION → Involved in clotting
What is haemostasis?
Means to reduce blood loss if a vessel wall is damaged.
How does haemostasis occur?
At the site, collagen is exposed.
3 stages:
1. Vascular spasm → constriction of vessel to reduce blood loss
- Platelet plug → platelets stick to exposed collagen, chemical released to encourage more platelets to the area - temporary seal
- Blood clotting → Involving a cascade of enzymes (clotting factors)
What is the extrinsic pathway of blood clotting?
Tissue damage releases tissue factor (+clotting factors) which leads to trigger of prothrombinase (enzyme).
What is the intrinsic pathway of blood clotting
When blood comes into contact with collagen, chemicals are released (+clotting factors)
which leads to trigger of prothrombinase (enzyme).
After prothrombinase has been triggered, what is the blood clotting process?
→ Prothrombinase transforms Prothrombin into Thrombin (enzyme).
→ Thrombin turns fibrinogen (soulble) → fibrin (insoluble)
→ These fibres are layed down and the clot is formed (inc. fibres, blood cells + platelets)
Calcium ions are required for this process
What is thrombosis?
Clotting in an unbroken vessel (usually a vein).
Why may thrombosis occur?
→ May be due to roughened endothelial surfaces resulting from atherosclerosis, trauma or infection
→ Blood flowing too slowly → clotting factors accumulate locally to initiate coagulation
→ The clot is called a thrombus - may dissolve spontaneously
↳ If it remains intact it may become dislodges - “embolus”
↳ An embolus in the artery - reduce blood supply to organ
↳ When an embolus lodges in lungs - pulmonary embolism
